1. Technical Field
Improved aerosol dispenser systems are disclosed. More specifically, aerosol dispenser systems using a compressed gas propellant to expel a liquid product from a container are disclosed wherein the compressed gas propellant is innocuous and VOC-free. Still more specifically, the nozzle, i.e., a combination of the insert and actuator body, are designed with one or more parameters optimized to provide an aerosol spray generated using a VOC-free propellant that has properties equivalent or comparable to that of an aerosol spray generated using a liquefied petroleum gas (LPG) propellant. As a result, an effective aerosol system is disclosed that provides a sufficiently small particle size without depending upon conventional hydrocarbon-based propellants.
2. Description of the Related Art
Aerosol dispensers have been commonly used to dispense personal, household, industrial, and medical products, and provide low cost, easy to use methods of dispensing products that are best used as an airborne mist or as a thin coating on surfaces. Typically, aerosol dispensers include a container, which holds a liquid product to be dispensed, such as soap, insecticide, paint, deodorant, disinfectant, air freshener, or the like. A propellant is used to discharge the liquid product from the container. The propellant is pressurized and provides a force to expel the liquid product from the container when a user actuates the aerosol dispenser by pressing an actuator button or trigger.
The two main types of propellants used in aerosol dispensers today include (1) liquefied gas propellants, such as hydrocarbon and hydrofluorocarbon (HFC) propellants, and (2) compressed gas propellants, such as compressed carbon dioxide or nitrogen. To a lesser extent, chlorofluorocarbon propellants (CFCs) have been used. The use of CFCs, however, has essentially been phased out due to the potentially harmful effects of CFCs on the environment.
In an aerosol dispenser using a liquefied petroleum gas-type propellant (LPG), the container is loaded with liquid product and LPG propellant to a pressure approximately equal to the vapor pressure of the LPG. After being filled, the container still has a certain amount of space that is not occupied by liquid. This space is referred to as the “head space.” Since the container is pressurized to approximately the vapor pressure of the LPG propellant, some of the LPG is dissolved or emulsified in the liquid product. The remainder of the LPG remains in the vapor phase and fills the head space. As the product is dispensed, the pressure in the container remains approximately constant as liquid LPG moves from the liquid phase to the vapor phase thereby replenishing discharged LPG propellant vapor.
In contrast, compressed gas propellants largely remain in the vapor phase. That is, only a relatively small portion of the compressed gas propellant is in the liquid-phase. As a result, the pressure within a compressed gas aerosol dispenser assembly decreases as the vapor is dispensed.
While this aspect is of using compressed gas propellants is disadvantageous, the use of compressed gas propellants may gain favor in the future as they typically do not contain volatile organic compounds (VOCs). Indeed, LPGs are considered to be a VOC thereby making their use subject to various regulations and therefore disadvantageous.
One way to reduce the VOC content in LPG-type aerosols is to reduce the amount of LPG used to dispense the liquid product without adversely affecting the product performance. Specifically, before the techniques of commonly assigned U.S. Pat. No. 7,014,127 to Valpey et al. (incorporated herein by reference), reducing the LPG content in commercial aerosol canned products resulted in excessive product remaining in the container after the LPG is depleted (“product r this etention”), increased particle size, and reduced spray rate, particularly as the container nears depletion. Techniques disclosed in the '127 patent provide a way to minimize the particle size of a dispensed product in order to maximize the dispersion of the particles in the air and to prevent the particles from “raining” or “falling out” of the air, while reducing the amount of liquefied gas-type propellant to 15-25% by weight. By reducing the amount of LPG in the container, the VOCs for the product are reduced.
The techniques of the '127 patent involve maintaining a Clark/Valpey (CV) value for the system at 25 or less, where CV=2.5(D−32)+10|Q−1.1|+2.6R, D is the average diameter in micrometers of particles dispensed during the first forty seconds of spray of the assembly, Q is the average spray rate in grams/second during the first forty seconds of spray of the assembly, and R is the amount of the product remaining in the container at the end of the life of the assembly expressed as a percentage of the initial fill weight.
A method of reducing the particle size for LPG aerosol systems is disclosed in commonly assigned U.S. Pat. No. 3,583,642 to Crowell et al., which is also incorporated herein by reference. The '642 patent discloses various spray heads or actuator bodies that incorporate a “breakup bar” for inducing turbulence in a product/propellant mixture prior to the mixture being discharged from the nozzle outlet orifice. Such turbulence contributes to reducing the size of the mixture particles discharged through the outlet orifice of the actuator body. While the '642 patent discloses one-piece actuator bodies with breakup bars, breakup bars have also been incorporated into smaller nozzle inserts that fit into actuator bodies.
To provide an alternative to LPG propellants and to eliminate any VOCs attributable to the propellant of an aerosol product, improved aerosol dispensing systems incorporating VOC-free compressed gas propellants are needed. However, to satisfy consumers, the employment of VOC-free compressed gas propellants should result in aerosols with properties equivalent or comparable to that of aerosols generated using LPG propellants. One such physical property for measuring the effectiveness of certain types and aerosols is the particle size or diameter as indicated by the Sauter Mean Diameter.
The Sauter Mean Diameter (also referred to as “D[3,2]”) is defined as the diameter of a droplet having the same volume/surface ratio as the entire spray. Conventional liquefied gas-type aerosol systems provide Sauter Mean Diameters at or below in 35 μm. If the performance of compressed gas propellant systems differ, users will observe the differences. These differences can be perceived to be beneficial or they can be related to efficacy. Sauter Mean Diameter is defined in a number of articles/presentations published by Malvern Instruments Limited (www.malvern.co.uk; see, e.g., Rawle, “Basic Principles of Particle Size Analysis”).
The small droplet size of conventional aerosol systems is obtained primarily by maintaining pressure in the aerosol can. When LPG propellant exits an aerosol can, it instantaneously changes phase from a liquid to a gas. When a liquid turns to a gas, the volume expands instantly by factors of a thousand or more. This resulting burst of energy breaks the liquid product carried with the propellant in the dispense stream into tiny droplets. Because compressed gas propellants are already in the gas phase, this burst of energy provided by liquid propellants is absent.
Published U.S. Patent Applications 2005/0023368 and 2006/0026817 both disclosed methods of designing improved aerosol spray dispensers that include optimizing certain parameters including vapor tap diameter, dip tube inner diameter, actuator body orifice dimensions, stem orifice diameter, land length, exit orifice size, and stem cross sectional area. However, these references are directed toward systems employing lower levels of VOCs, not the complete elimination of VOCs.
Thus, what is needed is an improved methodology for optimizing aerosol spray dispenser assemblies that rely upon VOC-free compressed gas propellants and improved nozzles (actuator bodies and swirl nozzle inserts) for use with VOC-free compressed gas propellants that provides the requisite properties (e.g., small particle size) and spray rate demanded by consumers.